I had got the iPhone XS 256Gb as soon as it was released and have been using it since then. I got one digital SIM and one physical SIM on my iPhone and it is working great.
Initially it had a serious problem of switching off the physical SIM, the one in the SIM slot of the phone, but after a few updates of iOS, that was sorted out. Now we can switch on and off the any SIM.
This month when I got my bill of the Indian mobile operator, I got bit shocked as it was more than my usual bill and I had not done any international roaming. When I checked the bill details, I found some calls in the international roaming. Yes I had traveled out of India, but I did not knowingly roam using the Indian mobile connection, but it happened due to a flaw which I think an iOS upgrade can sort out.
How did this happen?
Now this problem happens if both your lines are switched on.
What happens is every contact is assigned with a default calling line which I have set to the last used one. I do spend 15 days every month outside India so I have one SIM of an Indian operator and one from Maldives. As soon as I reach India, I change the default line and mobile data to the Indian SIM and when I go to Maldives, I change the default line and Data to the Maldives operator.
Now, the problem here is the default line is set to the last used one so when I make a call to someone from India using the Indian SIM the last used line is set to the Indian Operator and when I make the next call to the same person when I am in Maldives and my Indian SIM is switched on then the call would go from my Indian SIM which has an International roaming facility and I would not know, unless I am carefully looking at the icon showing the line used.
Solution for this
I feel if the iOS has a feature to give at least a warning that this call is going to be on International roaming or any better way to avoid such calls or always use the default line rather than last used line or any other assigned line.
So if you are using the iPhone digital SIMS then you should be careful about this.
I am not sure if there are any work around to sort this problem, please let me know in the comments if you had any such problems or if you have any solution for this issue.
Otherwise multiple digital SIMS are great options, I no longer have to open the phone cover and change my SIMS when my flight lands in another country.